Assembly 在mips中追加字符串

我应该读两个单独的字符串，计算长度，然后将第二个字符串放在第一个字符串末尾的新位置。我可以进行计数，并将第一个字符串保存到新位置，但在第二个字符串上，我只得到要追加的第一位。我不知道我的问题在哪里，提前谢谢

.data

    Prompt1:              .asciiz"\nPlease enter the first string.  "
    Prompt2:              .asciiz"\nPlease enter the second string.  "
    theString:            .asciiz"\nYou typed: \n"
    equalPrompt:          .asciiz"\nThe strings are equal\n"
    notEqualPrompt:       .asciiz"\nThe strings are not equal\n"
    stringLengthPrompt:   .asciiz"\nThe string length is: \n"
    stringAppend:         .asciiz"\nThe appended strings are: "
    stringAppend2:        .asciiz" "
    stringOne:  .space 100
    stringTwo:  .space 100


.text

    main:                           
    li  $t0,0
    jal getStrings
    la  $s4,stringOne
    jal stringLength
    move    $s0,$t0             #copy string one length
    la  $s4,stringTwo               
    jal stringLength
    move    $s1,$t0             #copy string two length
    la  $t5,stringOne
    la  $t6,stringTwo
    jal testEquality

    la  $t5,stringOne
    lb  $t1, 0($t5)
    jal append1

    la  $t6,stringTwo
    lb  $t1, 0($t6)
    jal append2
    j   end



getStrings:             

    li  $v0,4               
    la  $a0, Prompt1
    syscall

    li  $v0,8
    la  $a0, stringOne
    li  $a1, 40 
        syscall
                                #string one has been read in
    li  $v0,4               
    la  $a0, Prompt2
    syscall

    li  $v0,8
    la  $a0, stringTwo
    li  $a1, 40
        syscall 
                                #string two has been read in
    la  $a0,theString               #  "you typed:"
    li  $v0,4
    syscall

    la  $a0,stringOne
    li  $v0,4
    syscall

    la  $a0,stringTwo
    li  $v0,4
    syscall

    jr  $ra

end:    

    li  $v0,10
    syscall              

stringLength:                   #calculate length of strings to allocate memory

    li  $t0,0

stringLength1:

    lb  $t1, 0($s4)
    beqz    $t1,out
    addi    $s4,$s4, 1              #move position
    addi    $t0,$t0, 1              #counter
    j   stringLength1


out:

    la  $a0,stringLengthPrompt              
    li  $v0,4
    syscall

    move    $a0, $t0                #length of string 
    li  $v0,1
    syscall
    jr  $ra

equal:  

    la  $a0, equalPrompt
    li  $v0,4
    syscall

    jr  $ra

notEqual:   

    la  $a0, notEqualPrompt
    li  $v0,4
    syscall

    jr  $ra

testEquality:                       #test if both strings are equal

    lb  $t1, 0($t5)
    lb  $t2, 0($t6)                 
    bne $t1,$t2, notEqual
    addi    $t5,$t5,1                           
    addi    $t6,$t6,1   
    add $t7,$t1,$t2
    beqz    $t7,equal
    j   testEquality                    



append1:    

    add $s2,$s0,$s1

    move    $a0,$s2
    li  $v0,9
    syscall

    move    $t8,$v0
    move    $t9,$v0

append2:

    beqz    $t1,append3
    sb  $t1,0($t8)
    addi    $t5,$t5,1
    addi    $t8,$t8,1
    lb  $t1, 0($t5)
    b   append2

append3:

    beqz    $t1,appendOut
    sb  $t1,0($t9)
    addi    $t6,$t6,1
    addi    $t9,$t9,1
    lb  $t1, 0($t6)
    b   append3

appendOut:    

    li  $v0,4               
    la  $a0, stringAppend
    syscall

    move    $a0, $t9                
    li  $v0,4
    syscall

    jr  $ra

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调试你的代码怎么样？这个例子太长了，不需要任何人阅读。孤立这个问题，有人会很乐意看一看。